1. Field of the Invention
This invention relates to a magnetic recording disk employed as a recording medium for a magnetic recording apparatus such as an electronic still camera, particularly the present invention is directed to an improved central hub structure having a pulse generating member.
2. Description of the Background Art
A magnetic recording disk adapted to mount on an electronic still camera, which includes a magnetic recording medium and a central hub, is disclosed in Japanese laid-open patent publication No. 59-138063. FIGS. 7 to 15 illustrate such a conventional magnetic recording disk in which a magnetic recording medium 2 made of a flexible sheet material is retained on a central hub 1. Referring to FIG. 7, the central hub 1 includes a core member 10, a ring member 20, a leaf spring 30 and a covering member 40. The core member 10 having a central aperture 11 is formed by stamping a metal sheet made of soft iron and the like, as shown in FIG. 10. The ring member is made of synthetic resin and molded on the core member 10 so as to realize an integral hub body. The ring member 20 has a central aperture 21 which is approximately the same size as that of the core member 10. Both apertures of the core and ring members cooperate to form a center bore of the hub into which a spindle 3 of a disk driving mechanism is accomodated. On an inner periphery of the core member 10 are formed a pair of tapered portions 11a, 11a which are protruded inwardly into the aperture 11. A pair of shoulder portions 11b, 11b are also formed on the inner periphery to support the leaf spring 30. The core member 10 has a bent-up portion 12 which extends outwardly from the middle portion between the shoulder portions 11b, 11b in a direction perpendicular to a surface of the core member. A pulse generating portion which is a tip end 12a of the bent-up portion 12, is positioned opposed to a rotation detector (not shown in the drawings) of a disk driving mechanism. The rotation detector detects an amount of magnetic flux leak in a chucking magnet (not shown in the drawings) for the disk driving mechanism so that a rotational phase of the magnetic recording medium 2 is ascertained. A top face 12b of the pulse generating portion 12a is on the same plane as a top face 20b of the ring member 20.
In this case, the core member 10 is used as a yoke member which is attached to the chucking magnet. A notched portion 13 is provided at an outer peripheral edge of the core member 10 in order to keep a dynamic balance of rotating movement of the core member 10.
The aperture 21 of the ring member 20 has substantially a smaller diameter than that of the aperture 11 of the core member 10. As illustrated in FIGS. 12 to 14, at the tapered portions 11a, 11a which are protuberently formed on the inner periphery of the core member 10, the aperture 21 is larger in diameter than the aperture 11 of the core member 10. When the spindle 3 is inserted into the aperture 21, the leaf spring 30 supported on the shoulder portions 11b, 11b elastically biases the spindle 3 against the tapered portions 11a, 11a. As a result, the axis of the spindle 3 is consistent with the center of rotation of the magnetic recording medium 2. An inner peripheral surface 21a' of the ring member 20, which is in a lower position than the core member 10, is set flush with a distal end of the tapered portions 11a, 11a, as shown in FIG. 14. The spindle 3 is therefore protected from abrasion due to direct contact with edges of the tapered portions 11a, 11a, facilitating insertion and correct positioning of the spindle 3.
The ring member 20 is provided with a pair of slotted portions 22, 22. As illustrated in FIG. 12, each shoulder portion 11b of the core member 10 is positioned so as to project inwardly from an outside wall of each slotted portion 22 substantially up to the midway of the width of the slotted portion 22 to thereby assure that the leaf spring 30 being inserted is supported in the radial direction not by the outside wall of the slotted portion of the ring member 20 but by the shoulder portion of the core member 10. Moreover, the leaf spring 30 has a pair of tongue portions 30a, 30a which extend outwardly from both ends thereof and rest on the core member 10. This assures that the leaf spring is supported by the core member 10 in the axial direction of the spindle 3.
An outer diameter of the ring member 20 is consistent with an inner diameter of the magnetic recording medium 2. To this end, when assembled, an inner peripheral surface 2a of the magnetic recording medium 2 is snugly fitted over an outer peripheral surface 20a of the ring member 20. Upon molding of the ring member 20 on the core member 10, a rib member 50 is also molded along an outer peripheral portion of an underside 10b of the core member 10 as shown in FIG. 8. For the purpose of facilitating the molding of the rib member 50, a plurality of grooves 14 as illustrated in FIG. 10 are provided on an upper surface 10a of the core member 10.
In a process for manufacturing the central hub 1 for holding the magnetic recording medium 2, the leaf spring 30 is automatically inserted into the slotted portions 22, 22 of the ring members 20 after the ring member 20 is fixedly mounted on the core member 10. Subsequently, the magnetic recording medium 2 is fitted onto the outer peripheral surface 20a of the ring member 20 so that the under surface of the magnetic recording medium 2 closely contacts the upper surface 10a of the core member 10. The covering member 40 is fitted onto the outer peripheral surface 20a and then both members are attached to each other by high frequency welding whereby the magnetic recording medium 2 is retained between the covering member 40 and the core member 10. To this end, the magnetic recording disk with the central hub 1 as mentioned above is formed as an integrally configured body. Accordingly, the tongue portions 30a, 30a of the leaf spring 30 received in the slotted portions 22, 22 are covered with the covering member 40 so that the leaf spring 30 does not fall out therefrom. Such a magnetic recording disk with the central hub 1 is rotatably received in a housing of a flat box shape when used for example in a magnetic recording apparatus such as an electronic still camera.
As shown in FIG. 7, when the spindle 3 is inserted in the aperture 21 of the ring member 20, the spindle 3 is urged against the tapered portions 11a, 11a of the core member 10 by the biasing force of the leaf spring 30 located on the shoulder portions 11b, 11b. To this end, the spindle 3 is properly positioned such that the axis of the spindle 3 is consistent with the center of rotation of the magnetic recording medium 2. Further, in the magnetic recording disk with the central hub 1, a rotational phase of the magnetic recording medium 2 is determined by detecting a pulse generated by the top face 12b of the bent-up portion 12 which faces the rotation detector of the disk driving mechanism.
However, since the top face 20b of the ring member 20 is positioned on the same plane as the top face 12b of the core member 10 in the central hub 1 of the conventional magnetic recording disk as mentioned above, an area of the top face 12b may be undesirably reduced due to manufacturing inconsistencies or errors. Therefore, it is likely that the rotational phase of the magnetic recording medium 2 will not be accurately ascertained because the reduced area of the top face 12b induces decrease in an amount of pulse generation, making accurate detection thereof more difficult.